1. Field of the Invention
The invention relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaques from arteries, utilizing a rotational angioplasty device. In particular, the invention relates to improvements in a coupling between exchangeable drive shaft cartridge and prime mover carriage of a rotational angioplasty device.
2. Brief Description of Related Developments
A variety of techniques and instruments have been developed for use in the removal or repair of tissue in arteries and similar body passageways. A frequent objective of such techniques and instruments is the removal of atherosclerotic plaques in patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (i.e., under the endothelium) of a patient's blood vessels. Very often over time what initially is deposited as relatively soft, cholesterol-rich atheromatous material hardens into a calcified atherosclerotic plaque. Such atheromas restrict the flow of blood, and therefore often are referred to as stenotic lesions or stenoses, the blocking material being referred to as stenotic material. If left untreated, such stenoses can cause angina, hypertension, myocardial infarction, strokes and the like.
Rotational angioplasty procedures are a common technique for removing such stenotic material. Such procedures are used most frequently to commence the opening of cacifield lesions in coronary arteries. Often the rotational angioplasty procedure is not used alone, but is followed by a balloon angioplasty procedure. This, in turn, may frequently be followed by placement of a stent in order to prevent acute closure of the artery which has been opened.
Studies have shown, however, that a significant percentage of patients who have undergone balloon angioplasty and had a stent placed in an artery experience in-stent restenosis (i.e., blockage of the stent) which most frequently develops over a period of time as a result of excessive growth of scar tissue within the stent. Rotational angioplasty devices were utilized in removing the excessive scar tissue from the stents and, thereby were useful in providing assistance in restoring the patency of the arteries.
It should be understood that rotational angioplasty devices and rotational angioplasty procedures are often referred to as rotational atherectomy devices and rotational atherectomy procedures. These terms may be used interchangeably herein.
One example of a rotational angioplasty device is shown in U.S. Pat. No. 4,990,134 (Auth), wherein a front or distal portion of a burr is covered with an abrasive cutting material such as diamond particles. The burr itself is mounted at the distal end of a flexible drive shaft and is rotated at high speeds (typically, e.g., in the range of about 140,000-180,000 rpm) while it is advanced across the stenosis. Once the burr has been advanced across the stenosis, the artery will have been opened to a diameter equal to or only slightly larger than the maximum outer diameter of the burr. A series of different size burrs may be utilized to open the artery to a desired diameter. U.S. Pat. No. 5,314,438 (Shturman) shows another rotational angioplasty device having a drive shaft made from helically wound wires. A section of the drive shaft has an enlarged diameter. In one embodiment at least a front or distal segment of this enlarged diameter section is covered with an abrasive material to define an abrasive segment of the drive shaft. The enlarged diameter section is hollow. This Shturman Device described in the '438 patent is capable of opening an artery only to a diameter about equal to the maximum diameter of the enlarged diameter section of the drive shaft, thereby providing results similar to the Auth Device described in the '134 patent. Due to its flexibility the Shturman Device described in the '438 patent possesses certain advantages over the Auth Device described in the '134 patent. Another example of a rotational angioplasty device is provided in U.S. Pat. No. 6,132,444 issued to Shturman which describes a rotational atherectomy device having a flexible, elongated, rotatable drive shaft with an eccentric enlarged diameter section. At least part of the eccentric enlarged diameter section has a tissue removing surface with an abrasive surface to define a tissue removing segment of the drive shaft. When placed within an artery against stenotic tissue and rotated at sufficiently high speeds (e.g. in the range of about 60,000 rpm to about 200,000 rpm) the eccentric nature of the enlarged diameter section of the drive shaft causes such section to rotate in such a fashion as to open the stenotic lesion to a diameter substantially larger than the maximum diameter of the enlarged diameter section.
U.S. Pat. No. 5,314,407 (Auth) shows details of a type of handle which may be used in conjunction with rotational atherectomy devices of the type shown in the Auth '134 and Shturman '438 and '444 patents. A handle of the type shown in the Auth '407 patent has been commercialized by Heart Technology, Inc. (Redmond, Wash.), now owned by Boston Scientific Corporation (Natick, Mass.) in the rotational atherectomy device sold under the trademark Rotablator®. The handle of the Rotablator®. device includes a variety of components, including a compressed gas driven turbine, a mechanism for clamping a guide wire extending through the drive shaft, portions of a fiber optic tachometer, and a pump for pumping saline around the drive shaft.
The connection between the drive shaft (with its associated burr) and the turbine in the Rotablator®. device is permanent; yet, frequently it is necessary to use more than one size burr during an atherectomy procedure. That is, often a smaller size burr is first used to open a stenosis to a certain diameter, and then one or more larger size burrs are used to open the stenosis further. Such use of multiple burrs of subsequently larger diameters is sometimes referred to as a “step up technique” and is recommended by the manufacturer of the Rotablator® device. In the original multiple burr technique it was necessary to use a new Rotablator® device for each such successive size burr. Accordingly, there was a need for an atherectomy system that would permit a physician to use only one handle throughout an entire procedure and to attach to such handle an appropriate drive shaft and tissue removing implement (e.g., a burr) to initiate the procedure and then exchange the drive shaft and the tissue removing implement for a drive shaft having a tissue removing implement of a different size or even a different design.
A subsequent version of the Rotablator® device has been introduced with the ability to exchange a flexible distal portion of the drive shaft together with a burr for another distal portion of a drive shaft having a different size burr. Technical details of such a system are contained in international patent application No. WO 96/37153. This system utilizes a flexible drive shaft having a connect/disconnect feature allowing the physician to disconnect the exchangeable distal portion of the flexible drive shaft, together with the burr, from the flexible proximal portion of the drive shaft which is connected to the turbine of the handle, thus permitting the burr size to be changed without discarding the entire atherectomy unit.
Each exchangeable drive shaft portion is disposed within its own exchangeable catheter and catheter housing. The flexible proximal portion of the drive shaft in this system is permanently attached to the turbine and is not exchanged. This system has been commercialized by Boston Scientific under the trademark Rotablator®, RotaLink™ System. While the Rotablator® RotaLink™ System does permit one to change the burr size, the steps required to actually disconnect the exchangeable portion of the drive shaft and replace it with another exchangeable portion of the drive shaft are quite involved and require relatively intricate manipulation of very small components.
First, a catheter housing must be disconnected from the handle and moved distally away from the handle to expose portions of both the proximal and distal sections of the flexible drive shaft which contain a disconnectable coupling. This coupling is disconnected by sliding a lock tube distally, permitting complementary lock teeth on the proximal and distal portions of the flexible drive shaft to be disengaged from each other. A similar flexible distal drive shaft portion with a different burr may then be connected to the flexible proximal portion of the drive shaft. To accomplish such assembly, the lock tooth on the proximal end of the distal replacement portion of the drive shaft must first be both longitudinally and rotationally aligned with the complementary lock tooth at the distal end of the proximal portion of the drive shaft. Since the flexible drive shaft typically is less than 1 mm in diameter, the lock teeth are similarly quite small in size, requiring not insignificant manual dexterity and visual acuity to properly align and interlock the lock teeth. Once the lock teeth have been properly interlocked with each other, the lock tube (also having a very small diameter) is slid proximally to secure the coupling. The catheter housing must then be connected to the handle housing.
While this system does permit one to exchange one size burr (together with a portion of the drive shaft) for a burr of another size, the exchange procedure is not an easy one and must be performed with considerable care. The individual performing the exchange procedure must do so while wearing surgical gloves to protect the individual from the blood of the patient and to maintain the sterility of the elements of the system. Surgical gloves diminish the tactile sensations of the individual performing the exchange procedure and therefore make such exchange procedure even more difficult.
Accordingly, it would be desirable to have an atherectomy device permitting easier attachment and/or exchange of the drive shaft and its tissue removing implement.